Safety leg construction for a dockboard

ABSTRACT

An improved safety leg construction for a dockboard which restricts sudden gravitational descent of the ramp. Safety legs are mounted on the undersurface of the ramp and under conditions of slow descent of the ramp, the safety legs are moved to an inoperative position by upwardly biased cams. Under conditions of a sudden gravitational descent of the ramp, the increased downward velocity of the ramp and safety legs will overcome the biasing force on the cams thereby moving the cams to an inoperative position so that the safety legs will remain in an upright supporting position and engage fixed supports on the frame of the dockboard to limit further downward movement of the ramp. The invention also includes a provision for preventing the cams from camming the safety legs to a retracted position on upward rebound of the ramp following sudden descent.

United States Patent [191 Pfleger et al.

[4 1 Sept. 2, i975 SAFETY LEG CONSTRUCTION FOR A DOCKBOARD [75] Inventors: Robert H. Pfleger, Milwaukee;

Thomas J. Wiener, Brown Deer, both of Wis.; Klaus Fromme, Colorado Springs, C010.

[73] Assignee: Kelley Company, Inc., Milwaukee,

Wis.

[22] Filed: May 1, 1974 [21] Appl. No.: 465,913

[52] US. Cl. 14/711 [51] Int. Cl. 865G 11/00 [58] Field of Search 14/71, 72

[56] References Cited UNITED STATES PATENTS 3,117,332 1/1964 Kelley 14/71 3,137,017 6/1964 Pfleger 14/71 3,249,956 5/1966 Zajac 14/71 3,299,456 l/l967 Dieter.... 14/71 3,368,229 2/1968 Pfleger 1 14/71 3,500,486 3/1970 Le Clear... 14/71 3,530,488 /1970 Beckwith 14/71 an a Primary Examiner-Nile C. Byers, Jr. Attorney, Agent, or Firm-Andrus, Sceales, Starke & Sawall ABSTRACT An improved safety leg construction for a dockboard which restricts sudden gravitational descent of the ramp. Safety legs are mounted on the undersurface of the ramp and under conditions of slow descent of the ramp, the safety legs are moved to an inoperative position by upwardly biased cams. Under conditions of a sudden gravitational descent of the ramp, the increased downward velocity of the ramp and safety legs will overcome the biasing force on the cams thereby moving the cams to an inoperative position so that the safety legs will remain in an upright supporting position and engage fixed supports on the frame of the dockboard to limit further downward movement of the ramp. The invention also includes a provision for preventing the cams from camming the safety legs to a retracted position on upward rebound of the ramp following sudden descent.

36 Claims, 26 Drawing Figures PATENTED 2:975 3,902,213

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PATENTED 2975 3 902 213 sum 8 1F 8 SAFETY LEG CONSTRUCTION FOR A DOCKBOARD BACKGROUND OF THE INVENTION An adjustable dockboard as shown in the U.S. Pat. No. 3,137,017 includes a ramp having its rear edge hinged to a deck. The ramp is biased upwardly to an inclined position by a spring assembly and a manually releasable hold-down device holds the ramp against elevation. Hinged to the front edge of the ramp is an extension lip which is adapated to swing from a pendant position. in which the lip hangs downwardly from the front edge of the ramp, to an elevated position in which the lip forms an extension to the ramp. The lip, when in the extended position. is adapted to engage the bed of a truck or carrier and bridge the gap between the ramp and the truck to enable material handling equipment to move between the dockboard and the truck.

ln the dockboard. as disclosed in U.S. Pat. No. 3,137,017, the extension lip is automatically raised to its elevated position by a lip lifting and latching mechanism which is actuated by the upward movement of the ramp when the hold-down device is released. With the lip extended and the ramp in the upward inclined position, the ramp is walked down by the operator until the lip engages the bed of the truck. The engagement of the lip with the bed of the truck releases the weight from the lip latching mechanism. thereby releasing the latching mechanism so that when the truck pulls away from the dock the lip will automatically return to its pendant position.

To support the ramp in a generally horizontal or cross traffic position, cross traffic legs have been used in association with the ramp. U.S. Pat. No. 3,317,017 discloses cross traffic legs having spaced abutments adapted to engage fixed stops on the dock and act to support the ramp either in an upwardly inclined, above dock level position; a horizontal, cross traffic position; or a downwardly inclined, below dock level position.

In accordance with the disclosure of the aforementioned U.S. Pat. No. 3,137,017, the cross traffic legs are pivoted to the front edge of the ramp and are nor mally biased forwardly. The cross traffic legs of U.S. Pat. No. 3,137,017 are coupled to the lip, so that as the ramp is elevated and the lip is extended the cross traffic legs will automatically be pivoted to the rear. After loading. as the truck pulls away from the dock and the lip pivots downwardly from the extended to the pendant position, the cross traffic legs are urged forwardly to engage the fixed stops and prevent further descent of the ramp.

It has been found that in situations where the truck pulls away from the loading dock when a load, such as fork lift truck. or cargo. is on the ramp, the cross traffic legs could not respond quickly enough to catch or restrain the sudden dcsccnt of the ramp. Uncr conditions of sudden or rapid gravitational drop, through inertia. the lip of the ramp tends to maintain its extended position with respect to the ramp, thereby maintaining the cross traffic legs in the retracted position and prevent ing the legs from engaging the supporting stops.

The U.S. Pat. No. 3,368,229 is directed to a safety leg mechanism which is intended to prevent the sudden gravitational descent of the ramp caused by a load on the ramp when the truck pulls away from the dock. In accordance with the disclosure of U.S. Pat. No.

3,368,229. a tube is supported on the dock and a strut which moves up and down with the ramp is slidable within the tube. The strut has downwardly facing ratchet teeth which coact with a pawl on an escapemcnt device on the tube to support the ramp against descent and thereby prevent accidental descent of the ramp. An inertia responsive control for the escapement device keeps the pawl from engaging a ratchet tooth during gradual descent of the ramp, but on an initial sudden downward movement of the strut, the pawl engages the ratchet teeth and prevents the free downward movement of the ramp.

SUMMARY OF THE lNVENTlON The present invention relates to an improved safety leg mechanism for an adjustable, mechanical dockboard which restricts the sudden gravitational descent of the ramp. In accordance with the invention, one or more safety legs are hinged to the under surface of the forward edge of the ramp and are biased to a forward supporting position. In addition, cross traffic legs, similar to that disclosed in U.S. Pat. No. 3,137,017, can also be mounted on the forward edge of the ramp.

Under conditions of slow descent of the ramp, which can occur when the dockboard is walked down by the operator, or which can occur during a loading operation when the truck bed lowers due to the added load and the ramp descends to follow the lowering of the truck bed, the safety legs are pivoted rearwardly to a retracted. non'supporting position. by engagement with cams that are mounted on the supporting frame of the dockboard so that the safety legs will not interfere with the normal operation of the dockboard.

However. under conditions of sudden gravitational descent of the ramp, which can occur if a load is on the ramp when the truck pulls away from the dock, the lip will be in the extended position with the cross traffic legs retracted. The sudden descent of the ramp will tend to force the lip to remain in the extended position. thereby preventing the cross traffic legs from moving toward the forward supporting position. Due to the increased velocity produced by the sudden descent of the ramp with the added load, the inertia of the safety legs will overcome the biasing force on the same. thereby moving the cams to an inoperative position where the cams will not pivot the safety legs to a retracted'position. With the safety legs retained in their upright supporting position, they will engage supports on the frame thereby limiting the downward movement of the ramp.

The invention also includes a provision for preventing the cams from camming the safety legs to a retracted position on upward rebound of the ramp following sudden descent. On rapid descent of the ramp the safety legs will strike the supports on the frame. and depending on the acceleration of the ramp, the ramp may tend to rebound upwardly. During this upward rcbound, the cams will be returned to the operable position by the spring biasing force. and as the ramp again descends after the rebound. the cams may move the safety legs to the retracted position. thereby preventing the safety legs from enaging the supports on the frame. To prevent this action. a provision can be included to lock or retain the cams in the inoperative position so that the cams cannot cam the safety legs to a retracted position on rebound of the ramp.

The safety leg construction thereby provides protection against the uninterntional sudden descent of the ramp. and when combined with the standard corss traftie legs, the two mechanisms provide protection against descent of the ramp both gradually and suddenly.

The safety leg mechanism of the invention is less costly than prior devices of this type and minimizes the critcality of installation.

The safety leg construction provides a smooth operation, there being no resistance encountered due to the safety mechanism as the ramp is walked down by the operator to engage the lip with the truck bed.

Other objects and advantages will appear in the course of the following description DESCRIPTION OF THE DRAWINGS The drawings illustrate the best mode presently contemplated of carrying out the invention.

In the drawings:

FIG. 1 is a perspective view of a dockboard incorporating the safety leg mechanism of the invention with the ramp in the elevated position and the cross traffic legs retracted;

FIG. 2 is a side elevation of the dockboard taken along lines 2-2 of FIG. 1;

FIG. 3 is a front view of the structure, as shown in FIG. 2;

FIG. 4 is a side elevation of the dockboard with the ramp being supported by the cross traffic legs and the safety legs being cammed to the retracted position;

FIG. 5 is a side elevation similar to FIG. 4, showing the ramp being supported by the safety legs after a sudden gravitational drop;

FIG. 6 is an enlarged fragmentary side elevation showing the attachment of the cross traffic leg to the ramp;

FIG. 7 is a side elevation similar to FIG. 4, showing the lip supported on the bed of a truck and the ramp in an above dock level position;

FIG. 8 is a view similar to FIG. 7 and showing the lip supported on the bed of a truck and the ramp in at below dock level position;

FIG. 9 is a side elevation of a modified form of the invention incorporating a mechanism for preventing the safety legs from being cammed to the rear on upward rebound of the ramp;

FIG. 10 is a front view of the structure shown in FIG.

FIG. 11 is a view similar to FIG. 9 showing the cam member in the inoperative position following rapid descent of the ramp;

FIG. 12 is a side elevation ofa second modified form of the invention with the safety leg shown cammed to a retracted position;

FIG. 13 is a view taken along line l313 of FIG. 12;

FIG. 14 is a view similar to FIG. 12 showing the cam member in the inoperative position following rapid descent of the ramp;

FIG. 15 is a fragmentary front view of a further modified form of the invention incorporating a mechanism to lock the cam member in the inoperative position after rapid descent of the ramp;

FIG. 16 is a view taken along line I6l6 of FIG. 15;

FIG. 17 is a view similar to FIG. 15 and showing the cam member locked in the downward inoperative position;

FIG. 18 is a fragmentary side elevation of a further modified form of the invention utilizing a frangible pin in the safety leg;

FIG. 19 is a view taken along line 1919 of FIG. 18;

FIG. 20 is a view similar to FIG. 18 and showing one of the frangible pins fractured after rapid descent of the ramp;

FIG. 21 is a fragmentary side elevation of a further modified form of the invention;

FIG. 22 is a view similar to FIG. 21 and showing the safety leg in the upright supporting position following rapid descent of the ramp;

FIG. 23 is a section taken along line 23-23 of FIG. 22;

FIG. 24 is a fragmentary side elevation of another modified form of the invention;

FIG. 25 is a view similar to FIG. 24 and showing the safety leg in the upright supporting position following rapid descent of the ramp; and

FIG. 26 is a view taken along line 2626 of FIG. 25.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a dockboard 1 similar to that disclosed in US. Pat. No. 3,137,017, which is adapted to be mounted in a pit or depression in a loading dock. The dockboard 1 includes a frame 2 or supporting structure and a ramp 3 is hinged at its rear edge to the frame 2. The ramp 3 is adapted to be biased upwardly to an inclined position by a spring assembly 4. One end of the spring assembly 4 is connected to the supporting structure 2, while the opposite end of the spring assembly is connected to a lever arm 5. The upper end of the lever arm carries a roller that rides on a cam plate 6 mounted on the lower surface of the ramp 3.

The force of the spring assembly 4, if unrestrained, will act to pivot the lever arm 5 rearwardly, causing the upper end of the arm to ride against the cam plate 6 to thereby pivot the ramp to the upwardly inclined position, as shown in FIG. 1.

The ramp can be held in any desired position by means of a hold down mechanism 7, as disclosed in US. Pat. No. 3,137,017. The hold down mechanism 7 is a uni-directional device which prevents the upward movement of the ramp unless released, while permitting free downward movement of the ramp.

As illustrated in FIG. 1, an extension lip 8 is pivoted to the forward edge of the ramp. The lip 8 and ramp 3 carry aligned hinge tubes 9 which receive a hinge pin 10. With this construction the lip can be pivoted from the downwardly hanging pendant position to an extended position in which the ramp forms an extension to the surface of the ramp 3. Engagement of the rear edge of the lip with the forward surface of the ramp prevents the lip from moving beyond the extended position in which it is generally flush with the ramp.

The dockboard 1 also includes a lip lifting and latching mechanism 11 similar to that disclosed in US. Pat. Nos. 3,137,017 and 3,117,332. The lifting and latching mechanism serves to automatically move the lip from the pendant or downwardly hanging position to the extended position as the ramp is moved upwardly from the horizontal to the upwardly inclined position. The lip lifting and latching mechanism 11 also serves to latch or hold the lip in the partially extended position.

In the non-use position the upper surface of the ramp 3 will be generally horizontal or flush with the upper surface of the dock. After a truck is in position at the dock, the operator will release the hold down mechanism 7 through operation of a manually operated cable. thereby enabling the spring assembly 4 to pivot the ramp to the upwardly inclined position. As the ramp moves upwardly. the lip lifting and latching mechanism 1 1 will move the lip 8 to the partially extended position and latch the lip in this position. With the ramp 3 in the inclined position. as shown in FIG. 1, the operator then walks outwardly on the ramp and the weight of the operator in combination with the weight of the ramp will overcome the force of the spring assembly 4, thereby enabling the ramp to lower slowly until the lip 8 engages the bed of the truck or carrier. When the lip engages the truck bed. the lip will move to the fully extended position thereby releasing the lip latching mechanism and enabling the lip to freely pivot downwardly to the pendant position when the truck moves away from the dock.

The dockboard 1 can also include a pair of cross traffic legs 12 as disclosed in U.S. Pat. No. 3,137,617. Each of the cross traffic legs 12 is pivotally supported at the underside of the ramp and biased to a supporting or operating position by means of a torsion spring 13 which is wound around the hinge pin 14 that hinges the leg to the ramp. The cross traffic legs 12 are adapted to engage fixed supports 15 which are mounted on the frame 2.

As disclosed in U.S. Pat. No. 3,137,017. the cross traffic legs 12 can be provided with a series of notches 16. each of which is adapted to engage the upper end of the supports 15 to thereby support the ramp at various inclinations or elevations. For example. when the lower ends of the cross traffic legs 12 are engaged with the supports 15, the ramp 3 will be supported in a generally horizontal. cross traffic position. and when the notches 16 are engaged with the supports 15, the ramp will be supported at one of a number of below dock level positions.

As disclosed in U.S. Pat. No. 3,137,017, the cross traffic legs are adapted to be moved rearwardly to a retracted position in consequence of the lip 8 being moved from the pendant to the extended position. To retract the legs, a wiper arm 17 is secured to the forward surface of each of the legs 12 and is adapted to be engaged by roller 18 carried by a bracket 19 secured to one of the lip hinge tubes 9. When the lip is pendant, the roller 18 extends through an opening in the front header 20 of the ramp. As the lip 8 is pivoted upwardly to the extended position, the rollers 18 will act against the wiper arms 17 to pivot the cross traffic leg 12 to the retracted or rearward position.

When the truck. after the loading operation is completed. moves away from the loading dock, the unsupported lip 8 will pivot downwardly toward the pendant position. thereby enabling the torsion springs 13 to move the cross traffic legs toward the upright or supporting position where the legs. when the ramp is walked down by the operator. will engage the supports 15 to prevent further descent of the ramp. However. under certain conditions of sudden descent of the ramp. as may occur when the truck pulls away from the dock with a load. such as a lift truck or cargo on the ramp. the extension lip 8, due to inertia. will not immediately fall downwardly toward the pendant position. thereby maintaining the cross traffic legs 12 in the retracted position. so that the cross traffic legs will not be able to catch the sudden descent of the ramp.

In accordance with the invention. sudden gravitational descent of the ramp 3 is stopped by a safety mechanism which includes a pair of safety legs 21 that are hinged to the undersurface of the front edge of the ramp 3. To provide the hinge connection, the legs 21 are pivoted to the ramp 3 by means of hinge pins 22, and torsion spring 23 are wound around the hinge pins 22 and act to bias the legs 21 toward a forward or supporting position. Stops 24 are secured to the header 2(1 of the ramp and serve to limit the forward pivotal movement of the safety legs 21. The safety legs 21 are adapted to engage fixed supports 26 mounted on the frame 2 adjacent the supports 15, that are to be engaged by the cross traffic legs 12.

Each safety leg 21 has a pair of projections which extend laterally from the side surface of the respective leg. While the drawings illustrate the projections 15 to be in the form of generally cylindrical pins, it is contemplated that a roller or projection of other configura' tion can be utilized.

In accordance with the invention, cam members 27 are each pivotally connected between the side walls 28 of U-shaped brackets 29 which are mounted on the frame 2 adjacent the supports 26. Each cam member 27 is mounted for pivotal movement on a horizontal shaft 30 which extends between the side walls 28, and a torsion spring 31 acts to urge the cam member 27 upwardly or counterclockwise. as shown in FIG. 2. One end 32 of the spring 31 is engaged with the undersurface of the cam member 27, while the opposite end 33 of the torsion spring is engaged with the edge of one of the side walls 28. The rear end of each cam member 27 is provided with a nose or projection 34 which is adapted to engage a stop 35 connected to one of the side walls 28 to limit the rearward pivotal movement of the cam member under the force of the torsion spring 31.

The upper surface of the cam member 27 defines a cam surface 36 which is adapted to be engaged by the projection 25 on the correspondcing safety leg 21 as the ramp descends. Under conditions of a gradual or slow descent of the ramp. one of the projections 25 will ride along the cam surface 36, thereby pivoting the safety legs 21 to a retracted or rearward position. Under these conditions the retracted safety legs 21 will not interfere with the operation of the cross traffic legs 12. However. under conditions ofa sudden or rapid dcseent of the ramp. the inertia of the safety leg will overcome the force of the torsion springs 31, thereby pivoting the cam members 27 downwardly to a position beneath the level of the supports 26, instead of causing retraction of safety legs 21 as occurs under the slow descent of the ramp. so that the safety legs 21 will then engage the supports 26 to catch the ramp at a dock level position and prevent further downward movement of the ramp.

One or more shoulders 37 can be formed on the forward surface of each of the safety legs 21 and serve to engage the supports and limit the sudden descent of the ramp in situations where the ramp is below dock level when the truck pulls away from the dock.

In operation of the dockboard. the operator. after a truck has backed into position adjacent the dock. will manually release the hold down mechanism 7 thereby enabling the counter-balancing spring assembly 4 to pivot the ramp 3 to the upper inclined position. as shown in FIG. 1. As the ramp pivots upwardly, the lip lifting and latching mechanism 11 will act to move the lip from the pendant position to the partially extended position and to lock the lip in that position. As the lip 8 moves to the extended position, the rollers 18 ride against the wiper arms 17 to move the cross traffic legs 12 to the retracted position. The operator then walks outwardly on the inclined ramp causing the ramp to slowly lower until the lip 8 comes to rest upon the bed 38 of the truck. As the lip engages the truck bed 38, the lip will move to the fully extended position, thereby releaseing the lip latching mechanism and enabling the lip to pivot freely downward to the pendant position when the truck pulls away from the dock.

1f the truck bed is at a below dock level position the ramp, as it is walked down, will move to a downwardly inclined position, and in so doing, the lowermost projections 25 on safety legs 21 will engage the cams 27 to pivot the safety legs to a retracted non-interfering position.

When the truck pulls away from the dock after the loading operation is completed and if the ramp is above dock level and without an auxilliary load on the ramp, as illustrated in FIG. 7, the lip 8 will pivot downwardly from the extended to the pendant position, thereby enabling the cross traffic legs 12 to pivot forwardly under the force of the torsion springs 13 to the upright position. As the ramp is walked down by the operator, the lowermost 25 25 on the safety legs 21 will engage the cam members 27 and due to the slow descent of the ramp, the cam members will cam the safety legs 21 slightly rearward, as shown in FIG. 4, to a noninterfering position. Upon further lowering of the ramp, the lower ends of the cross traffic legs 12 will engage the supports 15 to support the dockboard in the horizontal cross traffic position.

Under conditions when the ramp is in an above dock level position, when the truck pulls away and an auxilliary load, such as a lift truck or cargo, is on the ramp, the ramp will descend suddenly, tending to swing the lip 8 to the extended position and thereby preventing the cross traffic legs 12 from moving forwardly to the supporting position. Under such conditions of high speed descent, the increased velocity of the ramp will act through the lower projections against the cam members 27 to overcome the biasing action of the springs 31, thereby pivoting the cam members 27 and maintaining the safety legs in the upright supporting position. The lower ends of the safety legs 21 will then engage the supports 26 to prevent further downward movement of the ramp.

1f the ramp is in a below dock level position when the truck pulls away from the dock, and an auxilliary load is on the ramp causing a sudden descent, the increased downward force caused by the increased velocity of the ramp will act through the upper projections 25 against the cam members 27 to overcome the force of the torsion springs 31, thereby pivoting the cam members 27 downwardly and enabling the shoulders 37 on the safety legs 21 to engage the upper ends of the supports 26 and limit further descent of the ramp.

The safety leg mechanism provides a simple and inexpensive device for limiting the sudden gravitational dcscent of the ramp as may occur if a truck pulls away from the dock and a load is on the ramp.

The drawings and the description have shown the safety legs 21 pivoted to the ramp and the fixed supports 26 associated with a dock. However, it is contemplated that this structure can be reversed with the pivotable legs being connected to the dock and the fixed legs or supports being associated with the ramp.

Further, while the description has shown a single shoulder 37 associated with the safety legs 21 to limit the downward movement of the ramp at 21 below dock level position, it is contemplated that a series of shoulders 37 or abutments can be provided on the safety legs which will catch the sudden gravitational drop of the ramp in a series of above and below dock level positions, and similarly, a series of cam-engaging projections 25 can be provided on the safety legs 21.

In addition, various types of biasing mechanisms can be used to urge the cam member 27 to the operative position. While the drawings illustrate the use of a torsion spring, it is contemplated that extension springs, compression springs or counter-balancing weights can be employed for this biasing function.

The safety leg construction of the invention also includes a provision for preventing the cams from camming the safety legs to a retracted position on upward rebound of a ramp following sudden descent. If the ramp descends rapidly, as previously described, the safety legs 21 will not be cammed to a retracted position, but instead will strike the supports 26 on the frame, and depending on the velocity of the descent, the ramp may tend to rebound upwardly. during this upward rebound, the cams 27 will be returned to the operable position through the spring biasing force. such as illustrated by springs 31. As the ramp again descends after rebound, the earns 27 which have returned to the operative position, will move the safety legs to the retracted position, thereby preventing the safety legs from engaging the supports 26 at the end of the rebound. To prevent this action, a provision can be included to lock or retain the cam members 27 in the in operative position, so that the cams cannot pivot the safety legs to a retracted position on rebound of the ramp.

FIGS. 9-11 illustrate a mechanism for maintaining the cams in the inoperative position on rebound of the ramp following rapid descent. As illustrated in FIGS. 9-11, a pair of safety legs 39, similar to legs 21, are pivotally connected to lugs 40 on the underside of ramp 3 by pins 41. Torsion spring 42, similar in structure to torsion spring 23, serves to urge the safety legs toward the upright supporting position.

Each of the safety legs 39 carries a pair of projections or pins 43, similar to projections 25 of the first embodiment, and during normal slow descent of the ramp, one of the pins 43, depending on the inclination of the ramp, will engage the cam member 44 to cam the leg to a retracted position. Under conditions of rapid, accelerated descent of the ramp, the safety legs 39 are adapted to engage fixed stops or legs 45, similar to legs 26 of the first embodiment.

Each cam member 44, which is similar in structure and operation to cam member 27, is pivoted to a vertical plate 46 through a shaft 47, and the front edge of the plate is welded to the angle iron at the front of the frame 2. Each cam member 44 is provided with an upper cam surface 48 which is adapted to be engaged by the pins 43 to cam the safety legs 39 to the retracted position on slow descent of the ramp, as previously described in the first embodiment.

The cam members 44 are urged or biased to an upwardly inclined position, as shown in FIG. 9 by an extension spring 49. One end 50 of the spring 49 is con nected to the frame 2., while the opposite end 51 of the spring 49 is attached to a cable 52 which extends around a pulley 53 and is secured to a connector 54 on lug 55. Lug 55 is secured to the shaft 47 and is located on the opposite side of the support plate 46 from the cam member 44.

Under normal conditions, the cam member 44 will be in an upwardly inclined position with the lug 55 being generally horizontal. The portion of the cable extending from the connector 54 to the pulley 53 will lie beneath the pivot axis of shaft 47, so that the force of the spring 49 acting through the cable 52 will tend to urge the cam member 44 upwardly, or counterclockwise, as shown in FIG. 9. To limit the upward movement of the cam member 44, a stop 57 is secured to the plate 46 and is adapted to be engaged by the-lower end of the cam member.

When the ramp descends at a normal slow rate, one of the pins 43, depending on the position of the ramp, will engage the upper surface 48 of the respective cam member 44, thereby pivoting or camming the safety leg 39 to the retracted position so that the safety leg will not interfere with the normal operation of the cross traffic legs. However, under a sudden or rapid gravitational descent, the increased velocity of the ramp will provide a greater downward force acting through the legs 39 on on the cam member 44, which will overcome the force of the spring 49, and move the cam member 44 to a downwardly inclined position as shown in FIG. 11. The safety leg 39 will then engage the support 45 to restrict further downward movement of the ramp.

With the cam member 44 in the downwardly inclined position, the portion of the cable 52 extending between the pulley 53 and the connector 54 is located above the pivot axis 47 so the force of the spring will now tend to urge the cam member 44 downwardly and prevent the return of the cam member to the upwardly inclined position. The downward pivotal movment of the cam member 44 is restricted by engagement with a stop 58 which is connected to the plate 46.

With this construction. if the ramp rebounds upwardly after striking the support 44, the cam member 44, being retained in the downwardly inclined position, cannot act to cam the safety legs 39 to the rear as the ramp and safety legs return downwardly after the rebound.

In order to return the cam member 44 to the upper operable position, a cable 59 is attached to the lug 55 and can extend upwardly to a pull loop, not shown, located on the upper side of the ramp. By manually pulling on the cable 59, the lug 55 and the attached cam member 44 will be pivoted to a point where the portion of the cable 52 located between the pulley 53 and the connector 54 extends beneath the pivot axis 47 so that the force of the spring 49 will then act to urge the cam member 44 to the upper inclined or operative position.

Alternatively. the cable 59 can be interconnected with the cable for the hold-down mechanism 7 so that release of the hold-down mechanism will also serve to return the cam member 44 to the operable position.

FIGS. 12-14 illustrate a modified form of the invention in which a linear moving cam member is utilized to calm the safety legs to a retracted position during normal slow descent of the ramp. As shown in FIGS. 12-14, a pair of safety legs 60, similar to legs 21, are pivotally connected to lugs 61, attached to the underside of the ramp, by pins 62. Torsion springs 63 are wound around the pins 62 and serve to urge or bias the legs 60 to an upright supporting position.

Engagement of the lower ends of the safety leg 60 with fixed supports 64 attached to the frame 2 will support or catch the ramp at a dock level position, while engagement of one of a series of notches or abutments 65 on the forward surface of each of the legs 60 will serve to catch the ramp at a series of below dock level positions.

Under normal slow descent of the ramp, the safety legs 60 are cammed to a retracted position by a cam member 66 having an upper inclined cam surface 67 which is adapted to be engaged by one of a series of pins 68 secured to the side of each leg 60. Pins 68 function in a manner similar to the pins 25 of the first embodiment, and depending on the inclination of the ramp at the time of the start of the descent, one of the pins 68 will engage and ride along the cam surface 67 to cam the legs 60 to the retracted position where they will not interfere with normal operation of the cross traffic legs 12, not shown in FIGS. 12-14.

Each of the cam members 66 is welded to a sleeve 69 which is mounted for vertical sliding movement on a shaft 70 which extends upwardly from the frame 2. The sleeve 69 and cam member 68 are biased upwardly by a coil spring 71. The upper end of the spring bears against the lower end of the sleeve 69 while the lower end of the spring rests on a spring seat 72 which is mounted on the shaft 70 through the retaining pin 73. The shaft 70 includes a pair of holes 74 and the pin 73 can be inserted in one of the holes 74, depending upon the spring force desired. By utilizing the uppermost of the two holes 74, the spring 71 will be in a more compressed state thcreby providing a greater biasing force against the cam member 66. Conversely, by locating the pin 73 in the lower hole 74, a lesser biasing force is achieved. In other situations where a further decrease in spring force is desired, the pin 73 can be omitted and the lower end of the spring 71 can bear against the frame 2.

Upward movement of the sleeve 69 and the cam member 66 is limited by engagement of a pin 75, which extends transversely through shaft 70, with the lower end of vertical slot 76 formed in the sleeve 69.

Under conditions of slow descent of the ramp, one of the pins 68 will ride against the surface 67 of cam member 66, depending on the angular disposition of the ramp, to thereby pivot the legs 60 to a retracted position, as previously described. However, under conditions of rapid gravitational descent the increased velocity of the ramp and legs will develop a force which will overcome the force of the spring 71, thereby causing the cam member 66 to move vertically downward to a position below the upper end of the support 64. Under these conditions and depending on the inclination of the ramp, either the lower end of the leg 60 or one of the notches 65 will engage the upper end of the support 64 to thereby limit further descent of the ramp.

The structure shown in FIGS. 12-14 also includes a mechanism which will prevent the cam member from camming the safety leg 60 to the rear on rebound of the ramp following a rapid descent. This mechanism includes a latch 77 which is pivotally connected by pin 78 to a bar 79 that is secured to the lower flange of one of the channel shaped beams 80 of ramp 3.

The forward end 81 of the latch extends a substantial distance beyond the pivot shaft 78 and is provided with a substantial mass so that the latch will normally be in a downwardly inclined position, as shown in FIG. 12.

Downward pivotal movement of the latch 77 is limited by engagement of a pin 82 with the portion of the latch bordering a hole 83. Pin 82 is connected to the bar 79.

A torsion spring 84 is wound around the pin 78 and one end of the torsion spring bears against the pin 82 while the opposite end of the torsion spring bears against the undersurfaee of a pin 85 that extends outwardly from the latch 77. Thus. the force of the torsion spring acts to pivot the latch upwardly, or counterclockwise as shown in FIG. 12., but the force of the torsion spring 84 is less than the moment produced by the weight of the latch 77 about pivot shaft 78, so that the latch will normally be in the downwardly inclined position. as shown in FIG. 12.

Under conditions of rapid descent of the ramp 3, the inertia of the latch will tend to swing the latch 77 upwardly with respect to the ramp, as shown in FIG. 14. The end 81 is provided with an upstanding abutment 86 which, on upward movement of the latch 77 relative to the ramp, is adapted to move behind one of a series of stop pins 87 which extends outwardly from the side of the leg 60. Thus, the engagement of the abutment 86 with one of the stop pins 87, as shown by the dashed lines in FIG. 12, will prevent the leg 60 form being moved to the rear or retracted by the cam member 66 on rebound of the ramp after a sudden graitational drop.

Under conditions of a slow normal descent of the ramp, the latch 77 will remain in the downwardly inclined or inoperable position, where the abutment 86 will not move behind the stop pins 87. It is only under the increased acceleration produced by the rapid gravitational drop of the ramp that the latch 77 will swing upwardly to the operable position to move the abutment 86 into engagement with one of the stop pins 87 to thereby restrict rearward pivotal movement of the leg 60. Thus, even though the ramp may rebound upwardly after a rapid drop and the cam member 66 returns upwardly through the force of the spring 71, the cam member cannot pivot the leg 60 to a retracted position due to the interference of the abutment 86 on the latch 77, and the legs 60 will return to engagement with the fixed supports 64. Once the legs 60 are resting on supports 64, the latches 77 will pivot by gravity to the downwardly inclined inoperable position.

FIGS. 1'7 illustrate a modified form of the invention in which the cam member is locked when moved to the inoperable position on rapid descent of the ramp so that the cam member cannot return to its operable position on rebound of the ramp.

The safety legs 60 and cam member 66 are utilized in the embodiment of FIGS. 15l7, but a cam locking pin 88 is utilized in place of the locking latch 77 of the previous embodiment. As best illustrated in FIG. 15, the fixed stop member or leg 64 is provided with a pair of side walls 89 and 90 and a central wall 91 which is spaced between the side walls. The upper edges of the walls 89-91 are connected by a top plate 92 which is adapted to be engaged by the lower end of the safety leg 60 to catch the ramp in a dock level position.

The pin 88 extends through aligned holes in the walls 89-91, and the pins is biased toward the cam member 66 by a spring 93'which extends between a spring seat 94 and the central wall 91. A retaining pin 95 extends through the locking pin 88 and serves to retain the seat 94 in position. The outer end of the locking pin 88 is formed with a relatively blunt tip 96 which is normally engaged with the side surfaces of the cam member 66. When the cam member is depressed on rapid descent of the ramp, as previously described, the end of the locking pin 88 will be received within a hole 97 in the cam member 66, thereby serving to retain the cam member in the lowered position. as shown in FIG. 17. With the cam member 66 locked in the lower or inoperative position, the cam member cannot move upwardly to a position where it could cam the safety leg 60 to a retracted position on rebound of the ramp following a fast gravitational descent.

The opposite end of the locking pin 88 is pivotally connected to a pair of links 98 and the links are pivotally connected to a bar 99 and to lugs 100 by pin 101. The opposite end of the bar 99 is provided with a hole 102 which receives a cable 103. By pulling the cable in the direction of the arrow in FIG. 13, the links 98 will be pivoted to retract the pin 88 from the hole 97 in the cam member to thereby permit the cam member to move to the upper operative position through the action of the spring 71. The cable 103 is adapted to be manually actuated through a pull ring located on the upper surface of the ramp 3. or alternately, the cable 103 can be attached to the cable for the holddown mechanism 7, so that on release of the holddown the cable 103 will be actuated to release the locking pin and permit the cam member to return ot its operative position.

FIGS. 18-20 illustrate a further modified form of the invention in which a frangible elment is associated with each safety leg and is adapted to engage a cam member to cam the safety legs to a retracted position on normal slow descent of the ramp, but is adapted to break on rapid descent of the ramp to maintain the safety leg in the upright supporting position. As shown in FIG. 18, a pair of safety legs 104, similar to legs 21 are pivoted to lugs 105, attached to the underside of the ramp 3, by hinge pins 106. Torsion springs 107, similar to springs 23, act to bias the safety legs 104 to the forward upright position.

Under conditions of rapid gravitational descent of the ramp, the lower ends of the legs 104 are adapted to seat upon fixed supports 108 attached to the frame 2. In addition. the legs are provided with one or more shoulders or abutments 109 which can seat upon the supports 108 under conditions when the ramp is subjected to a rapid gravitational drop when at an elevation below dock level. The abutments 109 operate in a manner similar to abutments 37 of the first embodiment.

A series of pins 110 are attached to the side surface of each of the legs 104 and are adapted to engage the upper inclined surface 111 of a fixed cam plate 112 which is secured to the frame 2. The pins 110 are frangible and are designed so that they will fracture or break when subjected to a predetermined force, such as that which would occur when the ramp is subjected to a rapid graviational drop. as for example. when a truck pulls away from the dock and a substantial added load is on the ramp.

As best illustrated in FIG. 19, each pin is provided with an outer enlarged head 113 which is adpated to engage the inclined cam surface 111. A neck portion 114 of reduced diameter is connected to the head 1 I3 and extends through an opening in the side wall of the leg 104. The inner end of the neck is provided with an enlargement 115 which will prevent the pin from mov ing outwardly through the hole in the leg. The pins can be formed of a plastic material. such as nylon or polyethylene. and the enlargements can be provided by heating the end of the pin to fuse the plastic and provide the enlarged stop or abutment. Alternately. the end of the neck 114 can be threaded to receive a nut or other fastener.

During normal slow descent of the ramp. one of the pins 110, depending on the inclination of the ramp. will engage the fixed cam surface 111 and will ride downwardly on the surface 111 causing the legs 104 to be pivoted rearwardly to the retracted position, as shown in FIG. 18. Thus. under normal slow descent of the ramp. the safety legs will be pivoted to the rear and will not interfere with the normal operation of the cross traffic legs 12, not shown. However. under conditions of sudden gravitational drop, as can occur when the truck pulls away from the dock and a heavy load or cargo is on the ramp. the increased acceleration caused by the added mass on the ramp will cause the pins 110 to engage the cams 111 with an increased force sufficient to break the pins and prevent the safety legs from being cammed rearwardly to the retracted position. With the pins being fractured. as shown in FIG. 20, the safety legs 104 will remain in the upright position and engage the fixed supports 108 to limit the sudden gravitational drop of the ramp.

After fracturing. replacement pins would have to be inserted in the holes in legs 104.

FIGS. 21-23 illustrate a further modified form of the invention which includes a pair of safety legs 116, similar to legs 21, that are pivoted to lugs 117, attached to the underside of the ramp 3, by hinge pins 118. The forward edge of each of the legs 116 is provided with a weight 119 and the position of the weight will tend to pivot the legs 1 16 rearwardly to a retracted position. as shown in FIG. 21. A stop 120 is secured to the ramp and limits the rearward pivotal movement of the leg 116. As illustrated in FIG. 21, the center of gravity of the safety leg I16. indicated by 121, is located forwardly of a vertical plan passing through the pivot axis 11), when the leg is engaged with the stop 120. With this construction. if the ramp is subjected to a sudden gravitational drop. the leg 116, due to the location of the center of gravity with respect to the pivot axis 1 18, will tend to swing forwardly to move the leg to an upright supporting position where the lower end of the leg 116 will engage a fixed support 122 on the frame 2, as shown in FIG. 22. However. if the ramp descends slowly. as under normal conditions. the leg 116 will not swing forwardly. but will be retained in the retracted position. as shown in FIG. 121. Thus. under normal slow descent. the safety leg 116 will remain retracted and will not interfere with the operation of the cross traffic legs 12, which are not shown in FIGS. 21-23.

The legs 116 can be provided with a series of abutments 123 or stops designed to engage the fixed support 112 at a series of above or below dock level positions.

FIGS. 24-26 illustrate a further modified form ofthe invention which includes a pair of safety legs 124, similar to legs 21, that are pivotally connected to lugs 125 attached to the underside of the ramp 3, by pins 126. Torsion springs 127 are wound around the pins 126 and serve to urge or bias the legs 124 forwardly to an upright supporting position.

Each of the safety legs 124 is composed of a pair of side members 128 and a central wall 129 which connects the side members. Each of the side members 128 is provided with a forwardly extending nose or abutment 130 and a bar 131 extends between the abutments of the respective side members.

During normal slow descent of the ramp 3, the safety legs 124 are automatically cammed or moved to a retracted position by means ofa cam member 132 having an upper inclined cam surface 133 that is adapted to be engaged either by the lower edge 134 of the central wall 129 or by the bar 131, depending upon the inclination of the ramp at the time the ramp is lowered. If the ramp is at an above dock level position when the truck pulls away from the dock. the lower edge 134 will engage the cam surface 133 to move the leg 124 to the retracted position. On the other hand, if the ramp is at at below dock level position when the truck pulls away from the dock, the bar 131 will engage the cam surface 133 to retract the safety leg.

Each of the cam members 132 is formed of a pair of plates 135 and the lower ends of the plates are bent outwardly away from each other and terminate in flanges 136, which are secured to a horizontal shaft 137. Shaft 137 is mounted for pivotal movement within openings in the side walls 138 of a fixed support 139 that is mounted on the frame 2 of the dockboard. In addition to the sidewalls 138, each support 139 includes a front wall 140 and a top channel member 141. The front wall 140 and the top channel 141 are provided with communicating slots 142 and 143, respectively. and the upper end of the cam member 132 extends through the slots 142 and 143.

Each cam member 132 is biased to a generally vertical position. as shown in FIG. 24, by a torsion spring 144. The end portions of torsion spring 144 are wound around pins 145 that extend inwardly from the side walls 138 of support 139. and the ends 146 of the torsion springs are secured within openings in studs 147 which are threaded within openings in the vertical flange of the top channel 141. Retaining nuts 148 are employed to retain the studs 147 in position.

The central portion of torsion spring 144 includes a pair of forwardly extending sections 149 which are connected together by the cross section 150. The section 149 of the torsion spring 144 bear against the ends of a pin 15] which extends through an opening in the cam member 132. Thus. the force of the torsion spring 144, when the cam member is in the upright position will act to pivot the cam member in a counterclockwise direction. as viewed in FIG. 24. The rearward pivotal movement of the cam member 132 is limited by engagement of the rear edge of the cam member with a stop pin 152 which extends inwardly from the depending flange of top channel 141.

Under conditions of normal slow descent of the ramp 3 either the lower edge 134 of central wall 129 or the bar the safety legs 124 in the upright supporting position. With the safety legs in the upright supporting position either the lower edge 134 or bar 131 will engage the top channel 141 of support 139 to restrict further downward movement of the ramp. With the cam member 132 pivoted forwardly, the force of the torsion spring 144 acting against the pin 151 will be located on a line disposed forwardly of the axis of shaft 137 with the result that the force of the torsion spring will act to bias the cam member 132 forwardly to the inoperative position. With the cam locked in the inoperative position, there is no possibility of the safety legs 124 being eammed to the rear on rebound of the ramp following the rapid descent.

Forward pivotal movement of the cam member 132 is limited by the engagement of the forward edge of the cam member with the edge 153 of slot 142.

The cam member 132 can be returned to the operative upright position, as shown in FIG. 26, by means of an operating cable 154 whic is attached to an arm 155 secured to the end of the shaft 137. The cable 154 can extend upwardly to a pull-ring located on the upper surface of the ramp, or alternately it can be attached to the cable employed to release the holddown mechanism 7 so that on release of the hold-down mechanism to permit the ramp to be elevated, the arm 155 will be simultaneously pivoted to thereby pivot the cam member 132 to the upright position, as shown in PK}. 24 and the force of the torsion spring 144 will act to bias or maintain the cam member in the upright or operating position.

We claim:

1. in a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a pivotablc leg mounted for pivotal movement on the second of said structures between an operable supporting position in which the leg is engaged with said support and a retractable inoperable position in which the leg is out of engagement with said support, means for biasing the leg to the operable supporting position, leg retracting means on said first structure and disposed to be engaged by the leg to move the leg to the retracted position on slow descent of the ramp structure from the inclined position toward the horizontal position whereby the leg will not interfere with further downward movement of the ramp structure, and means responsive to a predetermined rapid descent of the ramp structure for rendering the leg retracting means inoperative whereby the leg will not be moved to the retracted position and will be maintained in the operative position and engage the fixed support to prevent further descent of the ramp structure.

2. The dockboard construction of claim 1, wherein the leg retracting means includes a fixed cam on the first of said structures, and a frangible abutment connected to the leg and disposed to engage the cam, said abutment being fracturable upon rapid descent of the ramp structure to thereby render the leg retracting means inoperable so that the leg will be retained in the upright supporting position.

3. The dockboard construction of claim I, and including means for maintaining the leg retracting means in the inoperative condition following rapid descent of the ramp structure.

4. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a movable support secured to the second of said structures and disposed to engage said fixed support to thereby support said ramp structure at a given elevation, said movable support being mounted for movement between an operable supporting position and an inoperable non-supporting position, cam means connected to said first structure, said cam means having an operative position and a non-operative position, said cam means when in the operative position being disposed to engage the movable support as the ramp structure moves downwardly at a slow rate of descent from the inclined position toward the horizontal position and move said movable support to said non-supporting position, whereby said movable support will not interfere with further downward movement of the ramp structure, and means responsive to rapid descent of said ramp structure for moving said cam means to the nonoperative position, whereby the movable support will be maintained in the supporting position and engage the fixed support to prevent further descent of said ramp structure.

5. The dockboard construction of claim 4, wherein the cam means is mounted for linear movement between the operative and inoperative positions.

6. The dockboard construction of claim 4, and in cluding means for pivoting the movable support to said second structure, and biasing means for biasing the movable support to the supporting position.

7. The dockboard construction of claim 4, and including means for urging cam means to the operative position.

8. The dockboard construction of claim 4, and including a projection on the movable support disposed to engage the cam means and move the support means from the supporting position to the nonsupporting position as the ramp structure slowly descends.

9. The dockboard construction of claim 4, and including means for mounting the cam means for pivotal movement between said operative and non-operative positions, said cam means including an inclined cam surface disposed to be engaged by said movable support as the ramp structure descends, and biasing means for biasing the cam means to the operative position, said biasing means being arranged so that slow descent of the ramp structure will not overcome the force of said biasing means and the cam means will remain in the operative position and will move the movable support to the non-supporting position, said biasing means also being arranged so that rapid descent of the ramp structure will overcome the force of said biasing means to thereby move the cam means to the non-operative position and enable the movable support to engage the fixed support.

10. The dockboard construction of claim 4, wherein one of said supports includes a series of abutments disposed to engage the other of said supports to thereby support the ramp structure in a series of vertical positions.

ll. In a dockboard construction. a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position. a fixed leg secured to a first of said structures, a pivotable leg pivotally connected to a second of said structures and movable between a supporting position and a retracted position. said pivotable leg disposed to engage the fixed leg when in said supporting position to thereby support the ramp structure at a given elevation, cam means connected to the first structure and including a cam surface facing toward said pivotable leg, cam engaging means connected to the pivotable leg and disposed to engage the cam surface as the ramp structure is moved downwardly, said cam means being movable between an operative position and an inoperative position, biasing means for biasing the cam means to the operative position, said biasing means being arranged so that on descent of the ramp at a first speed engagement of said cam engaging means with the cam surface of said cam means pivots the pivotable leg to the retracted position and said biasing means being arranged so that on descent of said ramp at a second speed faster than said first speed, said cam engaging means will overcome the force of said biasing means to pivot said cam means to the inoperative position whereby said pivotable leg will be retained in the supporting position and will engage the fixed leg to prevent further descent of the ramp.

12. The dockboard construction of claim 1 1, wherein said pivotable leg is connected to the ramp structure. and said dockboard construction includes resilient means for urging said pivot-able leg to the supporting position.

13. The dockboard construction of claim 12, wherein the cam means is connected to the supporting structure and said cam surface extend upwardly and forwardly at an acute angle to the horizontal.

[4. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position position to an upwardly inclined position. an extension lip hinged to the forward edge of the ramp and movable between a downwardly hanging pendant position and an extended position where the lip forms an extension of the ramp, a first pair of legs including a first movable leg movably mounted to one of said structures and including a first fixed leg secured to the other of said structures and adapted to be engaged by said first movable leg to thereby support said ramp structure at a given elevation. said first movable leg being mounted for movement between a supporting position and a nonsupporting position, a second pair of legs including a second movable leg movably mounted to one of said structures and including a second fixed leg secured to the other of said structures and adapted to be engaged by said second movable leg to thereby support said ramp structure at a given elevation. said second movable leg being mounted for movement between a supporting position and a nonsupporting position. said first movable leg being operabl connected to the lip such that movement of the lip from the pendant to the extended position will move said first movable leg from the supporting position to the non-supporting position. leg moving means connected to the other of said structures and disposed to engage the second movable leg as the ramp structure moves dowmx'ardly from the inclined position, said leg moving means being responsive to descent of the ramp structure at a first speed for moving said second movable leg to the non-supporting position whereby said second movable leg will not interfere with further downward movement of the ramp structure and the ramp structure will be supported by engagement of the first movable leg with said first fixed leg, and means responsive to descent of the ramp at a second speed faster than said first speed for rendering said leg moving means inoperative, whereby the second movable leg will be maintained in the supporting position and will engage said second fixed leg to prevent further descent of the ramp structure.

15. The dockboard construction of claim 14, wherein said second movable leg is pivotally connected to the ramp structure. 7

16. The dockboard construction of claim 14, wherein said second movable leg is provided with a series of abutments with said abutments being engageable with said second fixed leg to support the ramp structure at a series of elevations.

17. The dockboard construction of claim 16, wherein a first of said abutments is on the end of said second movable leg facing said second fixed leg and a second of said abutments is located intermediate the ends of Said second movable leg, engagement of the first abutment with said second fixed leg will support the ramp structure in a generally horizontal position and engage ment of said second abutment with said second fixed leg will support the ramp structure at a downwardly inclined elevation.

18. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to said supporting structure, a pivotable leg mounted for movement about a pivot axis on the ramp structure between an operable supporting position in which the leg is engaged with said support and an inoperable position in which the leg is out of engagement with said support, biasing means for urging the leg to the inoperable position, stop means to limit the movement of the leg under the force of said biasing means and disposed to position the center of gravity of the leg is off-set spaced relation to a vertical plane passing through said pivot axis. said bising means exerting a force on said leg of sufficient magnitude such that on slow descent of the ramp structure. the leg will be retained in the inoperable position through the force of said biasing means and on rapid descent of the ramp structure, the inertia ofsaid leg will overcome the force of the biasing means to pivot the leg to the supporting position.

19. The dockboard construction ofclaim 18, wherein said biasing means comprises a weight mounted on the leg in a position so that the moment produced by the weight acting upon said pivot axis will urge the leg to the inoperable position.

20. The dockboard construction of claim 19, wherein the leg is mounted for pivotal movement on the ramp structure and said stop means is disposed on said ramp structure.

2 l. The dockboard construction ofclaim 19, wherein the weight is located on the upper portion of the forward side of the leg, and said leg includes a series of abutments spaced along said forward side and disposed to individually engage said fixed support to support the ram structure at a plurality of inclinations.

22. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizon tal position to an upwardly-inclined position, a fixed support connected to a first of said structures, a pivotable leg mounted for pivotal movement about a pivot axis on the second of said structures between an operable supporting position in which the leg is engaged with the fixed support and an inoperble position wherein the leg is out of engagement with said support, a fixed cam member connected to said first structure, and an abutment member on said leg and disposed to engage said cam member to thereby move the leg to the inoperable position on slow descent of the ramp structure, one of said members being constructed of a frangible material and arranged to fracture when subjected to an in creased force produced by rapid descent of the ramp structure to thereby maintain the leg in the supporting position.

23. The dockboard construction of claim 22, wherein said abutment member is constructed of frangible material and is provided with an enlarged head to engage the cam member and a neck portion of reduced thickness.

24. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a pivotable leg mounted for pivotal movement about a pivot axis on the second of said structures between an operable supporting position in which the leg is engaged with the fixed support and an inoperable position wherein the leg is out of engagement with said support, a cam on said first structure and movable between an operative position and an inoperative postion, biasing means to urge the cam to the operative position, an abutment on said leg disposed to engage the cam when the cam is in the operative position to thereby move the leg to the inoperable position on slow descent of the ramp structure, means responsive to rapid descent of the ramp structure for moving the cam to the inoperative position, whereby the leg will be retained in the supporting position and engage the fixed support to prevent further descent of the ramp structure, and holding means to retain the cam in the inoperative position following rapid descent of the ramp structure.

25. The dockboard construction of claim 24, and including means to manually release the holding means, whereby the biasing means will move the cam to the operative positionv 26. The dockboard construction of claim 24, wherein said holding means comprises a first locking element on said cam and a second locking element on said first structure, said locking elements being engageable when the cam is moved to the inoperative position.

27. The dockboard construction of claim 26, wherein one of said locking elements comprises a spring loaded pin and the other of said locking elements comprises an abutment member to be engaged by said pin.

28. The dockboard construction of claim 27, and including manual means to release the pin from engagement with said abutment member.

29. The dockboard construction ofclaim 24, wherein said holding means comprises an acceleration responsive latch member movable between a latching position and a release position, means to bias the latch member to the released position, means responsive to rapid descent of said ramp structure to move said latch member from the released position to the latching position, and abutment means on said leg to be engaged by said latch member when in the latching position to thereby prevent retraction of said leg on upward rebound of the ramp structure.

30. The dockboard construction of claim 29, wherein said latching member is mounted for pivotal movement with respect to said second structure about a pivot axis, and said biasing means comprises a weight connected to said latching member and disposed to pivot said latching member in a first direction about said pivot axis to the release position, rapid descent of the ramp structure causing said latching member to rotate in the opposite direction about said pivot axis to said latching position.

31. The dockboard construction of claim 30, wherein said abutment means comprises a series of spaced projections with each projection disposed to bebe by said latching member at various elevations of said ramp structure.

32. The dockboard construction of claim 24, wherein said holding means comprises a toggle mechanism connected to the cam and having a first position and a second position. said toggle mechanism when in said first position acting to urge the cam to the operative position and said toggle mechanism when in said second position acting to urge the cam to the inoperative position, said toggle mechanism being moved to the second position as the cam is moved to the inoperative position on rapid descent of the ramp structure.

33. The dockboard construction ofclaim 32, wherein said toggle mechanism includes a resilient member connected to said first structure, and a connecting member connecting the resilient member to said cam.

34. The dockboard construction ofclaim 33, wherein said resilient member comprises an extension spring and the connecting member comprises a cable.

35. The dockboard construction of claim 32, wherein said toggle mechanism includes a torsion spring connecting said first structure and the cam.

36. The dockboard construction of claim 32, and including manual means to move the cam from the inoperative position to the operative position, and means operably connecting the toggle mechanism and said cam so that movement of said cum from the inoperative position to the operative position will act to move the toggle mechanism from the second position to the first position.

Q i t. v..-

UNRTED STATES PATENT OFFICE C'HEECATE tnhtcrtw o PATENYNO. 3,902,213

DATED September 2, 1975 ihvniroiiisi ROBERT H. PFLEGER, THOMAS J. WIENER & KLAUS FROMME it is certified that error appears in the ah0ve-identitied patent and that said Letters Patent are he aefiv corrected as shown below:

Col. 2 Line 67 Cancel "corss" and substitute therefor --cross-- i Col. 7 Line 25 Cancel "25", first occurrence, and substitutei therefor projections--- Col. 13 Line 35 Before 'edge" insert --upper-- Col. 14 Line 46 Cancel "section" and substitute therefor 3 --sections- Col. 15 Line 31 Before "We Claim" insert the following paragraph -Various modes of carrying out the invention are contemplated as being Q within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.--- Col. 16 Line 35 After "urging"-insert ---the--- i Col. 17 Line 32 Cancel "extend" and substitute therefor Q 2 -extends- Col. 18 Line 41 Cancel "is" and substitute therefor -in Col. lb Line 42 Cancel "bising" and substitute therefor biasing--- Col. 18 Line 64 Cancel "ram" and substitute therefor --ramp--- Col. 19 Line 6 Cancel "inoperble" and substitute therefor Q -inoperable- Col. 19 Line 33 After "inoperative" cancel "postion" and substitute therefor --position--- Col. 20 Line 26 Cancel "be", second occurrence, and substitute therefor --engaged-- 7 I 0 I rgned an rated this i [SEAL] y-zhirai -ay 0f March 197 Arrest.

RUTH C. MASON Arresting Officer C. MARSHALL DANN ummissiuner oj'larenls and Trademarks 

1. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a pivotable leg mounted for pivotal movement on the second of said structures between an operable supporting position in which the leg is engaged with said support and a retractable inoperable position in which the leg is out of engagement with said support, means for biasing the leg to the operable supporting position, leg retracting means on said first structure and disposed to be engaged by the leg to move the leg to the retracted position on slow descent of the ramp structure from the inclined position toward the horizontal position whereby the leg will not interfere with further downward movement of the ramp structure, and means responsive tO a predetermined rapid descent of the ramp structure for rendering the leg retracting means inoperative whereby the leg will not be moved to the retracted position and will be maintained in the operative position and engage the fixed support to prevent further descent of the ramp structure.
 2. The dockboard construction of claim 1, wherein the leg retracting means includes a fixed cam on the first of said structures, and a frangible abutment connected to the leg and disposed to engage the cam, said abutment being fracturable upon rapid descent of the ramp structure to thereby render the leg retracting means inoperable so that the leg will be retained in the upright supporting position.
 3. The dockboard construction of claim 1, and including means for maintaining the leg retracting means in the inoperative condition following rapid descent of the ramp structure.
 4. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a movable support secured to the second of said structures and disposed to engage said fixed support to thereby support said ramp structure at a given elevation, said movable support being mounted for movement between an operable supporting position and an inoperable non-supporting position, cam means connected to said first structure, said cam means having an operative position and a non-operative position, said cam means when in the operative position being disposed to engage the movable support as the ramp structure moves downwardly at a slow rate of descent from the inclined position toward the horizontal position and move said movable support to said non-supporting position, whereby said movable support will not interfere with further downward movement of the ramp structure, and means responsive to rapid descent of said ramp structure for moving said cam means to the non-operative position, whereby the movable support will be maintained in the supporting position and engage the fixed support to prevent further descent of said ramp structure.
 5. The dockboard construction of claim 4, wherein the cam means is mounted for linear movement between the operative and inoperative positions.
 6. The dockboard construction of claim 4, and including means for pivoting the movable support to said second structure, and biasing means for biasing the movable support to the supporting position.
 7. The dockboard construction of claim 4, and including means for urging cam means to the operative position.
 8. The dockboard construction of claim 4, and including a projection on the movable support disposed to engage the cam means and move the support means from the supporting position to the non-supporting position as the ramp structure slowly descends.
 9. The dockboard construction of claim 4, and including means for mounting the cam means for pivotal movement between said operative and non-operative positions, said cam means including an inclined cam surface disposed to be engaged by said movable support as the ramp structure descends, and biasing means for biasing the cam means to the operative position, said biasing means being arranged so that slow descent of the ramp structure will not overcome the force of said biasing means and the cam means will remain in the operative position and will move the movable support to the non-supporting position, said biasing means also being arranged so that rapid descent of the ramp structure will overcome the force of said biasing means to thereby move the cam means to the non-operative position and enable the movable support to engage the fixed support.
 10. The dockboard construction of claim 4, wherein one of said supports includes a series of abutments disposed to engage the other of said supports to thereby support the ramp structure in a series of vertical positions.
 11. In a dockboard construction, a supPorting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed leg secured to a first of said structures, a pivotable leg pivotally connected to a second of said structures and movable between a supporting position and a retracted position, said pivotable leg disposed to engage the fixed leg when in said supporting position to thereby support the ramp structure at a given elevation, cam means connected to the first structure and including a cam surface facing toward said pivotable leg, cam engaging means connected to the pivotable leg and disposed to engage the cam surface as the ramp structure is moved downwardly, said cam means being movable between an operative position and an inoperative position, biasing means for biasing the cam means to the operative position, said biasing means being arranged so that on descent of the ramp at a first speed engagement of said cam engaging means with the cam surface of said cam means pivots the pivotable leg to the retracted position and said biasing means being arranged so that on descent of said ramp at a second speed faster than said first speed, said cam engaging means will overcome the force of said biasing means to pivot said cam means to the inoperative position whereby said pivotable leg will be retained in the supporting position and will engage the fixed leg to prevent further descent of the ramp.
 12. The dockboard construction of claim 11, wherein said pivotable leg is connected to the ramp structure, and said dockboard construction includes resilient means for urging said pivotable leg to the supporting position.
 13. The dockboard construction of claim 12, wherein the cam means is connected to the supporting structure and said cam surface extend upwardly and forwardly at an acute angle to the horizontal.
 14. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position position to an upwardly inclined position, an extension lip hinged to the forward edge of the ramp and movable between a downwardly hanging pendant position and an extended position where the lip forms an extension of the ramp, a first pair of legs including a first movable leg movably mounted to one of said structures and including a first fixed leg secured to the other of said structures and adapted to be engaged by said first movable leg to thereby support said ramp structure at a given elevation, said first movable leg being mounted for movement between a supporting position and a non-supporting position, a second pair of legs including a second movable leg movably mounted to one of said structures and including a second fixed leg secured to the other of said structures and adapted to be engaged by said second movable leg to thereby support said ramp structure at a given elevation, said second movable leg being mounted for movement between a supporting position and a non-supporting position, said first movable leg being operably connected to the lip such that movement of the lip from the pendant to the extended position will move said first movable leg from the supporting position to the non-supporting position, leg moving means connected to the other of said structures and disposed to engage the second movable leg as the ramp structure moves downwardly from the inclined position, said leg moving means being responsive to descent of the ramp structure at a first speed for moving said second movable leg to the non-supporting position whereby said second movable leg will not interfere with further downward movement of the ramp structure and the ramp structure will be supported by engagement of the first movable leg with said first fixed leg, and means responsive to descent of the ramp at a second speed faster than said first speed for rendering said leg moving means inoperative, whereby the second movable leg will be maintained in the supporting position and will engage said second fixed leg to prevent further descent of the ramp structure.
 15. The dockboard construction of claim 14, wherein said second movable leg is pivotally connected to the ramp structure.
 16. The dockboard construction of claim 14, wherein said second movable leg is provided with a series of abutments with said abutments being engageable with said second fixed leg to support the ramp structure at a series of elevations.
 17. The dockboard construction of claim 16, wherein a first of said abutments is on the end of said second movable leg facing said second fixed leg and a second of said abutments is located intermediate the ends of said second movable leg, engagement of the first abutment with said second fixed leg will support the ramp structure in a generally horizontal position and engagement of said second abutment with said second fixed leg will support the ramp structure at a downwardly inclined elevation.
 18. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to said supporting structure, a pivotable leg mounted for movement about a pivot axis on the ramp structure between an operable supporting position in which the leg is engaged with said support and an inoperable position in which the leg is out of engagement with said support, biasing means for urging the leg to the inoperable position, stop means to limit the movement of the leg under the force of said biasing means and disposed to position the center of gravity of the leg is off-set spaced relation to a vertical plane passing through said pivot axis, said bising means exerting a force on said leg of sufficient magnitude such that on slow descent of the ramp structure, the leg will be retained in the inoperable position through the force of said biasing means and on rapid descent of the ramp structure, the inertia of said leg will overcome the force of the biasing means to pivot the leg to the supporting position.
 19. The dockboard construction of claim 18, wherein said biasing means comprises a weight mounted on the leg in a position so that the moment produced by the weight acting upon said pivot axis will urge the leg to the inoperable position.
 20. The dockboard construction of claim 19, wherein the leg is mounted for pivotal movement on the ramp structure and said stop means is disposed on said ramp structure.
 21. The dockboard construction of claim 19, wherein the weight is located on the upper portion of the forward side of the leg, and said leg includes a series of abutments spaced along said forward side and disposed to individually engage said fixed support to support the ram structure at a plurality of inclinations.
 22. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a pivotable leg mounted for pivotal movement about a pivot axis on the second of said structures between an operable supporting position in which the leg is engaged with the fixed support and an inoperble position wherein the leg is out of engagement with said support, a fixed cam member connected to said first structure, and an abutment member on said leg and disposed to engage said cam member to thereby move the leg to the inoperable position on slow descent of the ramp structure, one of said members being constructed of a frangible material and arranged to fracture when subjected to an increased force produced by rapid descent of the ramp structure to thereby maintain the leg in the supporting position.
 23. The dockboard construction of claim 22, wherein said abutment member is constructed of frangible material and is provided with an enlarged head to engage the cam member and a neCk portion of reduced thickness.
 24. In a dockboard construction, a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable from a generally horizontal position to an upwardly inclined position, a fixed support connected to a first of said structures, a pivotable leg mounted for pivotal movement about a pivot axis on the second of said structures between an operable supporting position in which the leg is engaged with the fixed support and an inoperable position wherein the leg is out of engagement with said support, a cam on said first structure and movable between an operative position and an inoperative postion, biasing means to urge the cam to the operative position, an abutment on said leg disposed to engage the cam when the cam is in the operative position to thereby move the leg to the inoperable position on slow descent of the ramp structure, means responsive to rapid descent of the ramp structure for moving the cam to the inoperative position, whereby the leg will be retained in the supporting position and engage the fixed support to prevent further descent of the ramp structure, and holding means to retain the cam in the inoperative position following rapid descent of the ramp structure.
 25. The dockboard construction of claim 24, and including means to manually release the holding means, whereby the biasing means will move the cam to the operative position.
 26. The dockboard construction of claim 24, wherein said holding means comprises a first locking element on said cam and a second locking element on said first structure, said locking elements being engageable when the cam is moved to the inoperative position.
 27. The dockboard construction of claim 26, wherein one of said locking elements comprises a spring loaded pin and the other of said locking elements comprises an abutment member to be engaged by said pin.
 28. The dockboard construction of claim 27, and including manual means to release the pin from engagement with said abutment member.
 29. The dockboard construction of claim 24, wherein said holding means comprises an acceleration responsive latch member movable between a latching position and a release position, means to bias the latch member to the released position, means responsive to rapid descent of said ramp structure to move said latch member from the released position to the latching position, and abutment means on said leg to be engaged by said latch member when in the latching position to thereby prevent retraction of said leg on upward rebound of the ramp structure.
 30. The dockboard construction of claim 29, wherein said latching member is mounted for pivotal movement with respect to said second structure about a pivot axis, and said biasing means comprises a weight connected to said latching member and disposed to pivot said latching member in a first direction about said pivot axis to the release position, rapid descent of the ramp structure causing said latching member to rotate in the opposite direction about said pivot axis to said latching position.
 31. The dockboard construction of claim 30, wherein said abutment means comprises a series of spaced projections with each projection disposed to be be by said latching member at various elevations of said ramp structure.
 32. The dockboard construction of claim 24, wherein said holding means comprises a toggle mechanism connected to the cam and having a first position and a second position, said toggle mechanism when in said first position acting to urge the cam to the operative position and said toggle mechanism when in said second position acting to urge the cam to the inoperative position, said toggle mechanism being moved to the second position as the cam is moved to the inoperative position on rapid descent of the ramp structure.
 33. The dockboard construction of claim 32, wherein said toggle mechanism includes a resilient member connected to said first structure, and a connecting member connecting the resiliEnt member to said cam.
 34. The dockboard construction of claim 33, wherein said resilient member comprises an extension spring and the connecting member comprises a cable.
 35. The dockboard construction of claim 32, wherein said toggle mechanism includes a torsion spring connecting said first structure and the cam.
 36. The dockboard construction of claim 32, and including manual means to move the cam from the inoperative position to the operative position, and means operably connecting the toggle mechanism and said cam so that movement of said cam from the inoperative position to the operative position will act to move the toggle mechanism from the second position to the first position. 